A new assessment of Madagascar’s Coffea species shows which traits reflect phylogenetic signal

On the island of Madagascar, the genus Coffea has diversified into 66 endemic species that occupy differing environments and vary in their morphology and reproduction. Many are restricted to one or a few forests, leaving them vulnerable to natural disasters and human activity. Over 80% of Coffea species globally are listed on the IUCN Red List, ranging from ‘Near Threatened’ to ‘Critically Endangered’.

The 66 Madagascan species, on the whole, are well-differentiated morphologically, but poorly distinguished genetically. This may be due to either the absence of strong genetic barriers, allowing gene flow among species, or recent speciation with rapid morphological divergence. Both may also be true. A better understanding of the distribution of phenotypic traits and reproductive strategies is important to improving conservation measures for this genus.

In a recent article published in Annals of Botany, lead author Aurore Rimlinger and colleagues studied the morphological, phenological, and functional traits of 36 species of Madagascan wild Coffea growing in a large ex situ collection. The authors then compared these traits to a completely resolved molecular phylogeny of the genus. The use of ex situ specimens in a common garden helped to separate genetically determined traits from those heavily influenced by the growing environment by minimizing environmental differences.

The researchers found that when grown ex situ, the number of days-to-blossoming after a triggering rain was well-conserved among species, indicating a strong genetic component. Asynchronous responses among species would help to erect barriers to hybridization. Other traits that showed a strong phylogenetic signal include the ratio of internode mass to leaf mass, stomatal length and density, and stem size.

The authors note that their results “highlight the role of ex situ collections, which gather large numbers of accessions living under common conditions, not only as repositories of species diversity but also as potential sources of common garden experiments, offering an important opportunity to describe phenotypic and inter-annual variation.”